L.A. County prosecutors have built their case around a sheriff's deputy who told investigators he witnessed the beating and later met with other deputies to discuss how to cover it up, records show.

The Los Angeles County district attorney's office has quietly filed assault charges against three sheriff's deputies accused of punching and kicking a jail inmate after he was disrespectful to a guard, according to court records.

Prosecutors have built their case around a sheriff's deputy who told investigators he witnessed the beating and later met with other deputies to discuss how to cover it up, the records show.

The charges mark a rare criminal filing against deputies working in the jails: It is the third excessive-force prosecution of jail deputies in a decade, according to law enforcement records and interviews. Inmates frequently allege that deputies have used excessive force, but law enforcement officials say such cases are difficult to prove or prosecute.

Inmate Gabriel Vasquez had a fractured cheekbone and injuries to his left ear, rib cage and face in the January 2006 incident. Sheriff's investigators initially discounted his claim that deputies caused the injuries, concluding that they were either self-inflicted or caused by other inmates, according to court records.

But investigators reopened the case after learning that a deputy who had denied seeing any injuries to Vasquez later admitted during a job interview with another police agency that he had lied about a use of force in the jail.

In a second interview with internal affairs, the deputy, Ryan Lopez, said three deputies took part in the beating. Lopez testified before a grand jury last year and was offered immunity from prosecution in exchange for truthful testimony, records say.

Prosecutors filed assault charges in September against Lee Simoes, 34; Humberto Magallanes, 29; and Kenny Ramirez, 30. The three deputies have pleaded not guilty and are on administrative leave without pay.

"This is another stark reminder that nobody is above the law," said sheriff's spokesman Steve Whitmore.

The district attorney's office typically releases a press statement when serious charges are filed against law enforcement officers but did not do so in this case. "We feel that the public has a right to know about these cases," said Sandi Gibbons, a spokeswoman in the district attorney's office. She said the Justice System Integrity Division, which is handling the case, did not notify her about the filing, despite an office policy requiring such notice.

Vicki I. Podberesky, an attorney representing Ramirez, said the accused deputies deny using force on the inmate. Vasquez, she said, told jail staff that he suffers from hallucinations, hears voices and has a history of mental illness.

Podberesky said she believed it was highly unlikely that deputies would hurt an inmate without writing a report to justify their use of force.

"To beat somebody up and throw him in a cell and wait for the next round of deputies to come on duty, it just doesn't make any sense," she said.

Peter J. Eliasberg, managing attorney with the American Civil Liberties Union of Southern California, said his organization receives an average of three or four inmate complaints about excessive force each week. Many of those who complain to the ACLU later decide not to report to the Sheriff's Department, fearing retaliation, he said.

Michael Gennaco, the chief attorney with the Office of Independent Review, which monitors discipline of sheriff's deputies, said such complaints are less common today than they were 10 or 20 years ago. He said the department has strengthened enforcement of rules that require deputies to write reports when they use force and prohibit them from entering an unruly inmate's cell without a supervisor.

Gennaco, a former assistant U.S. attorney, said prosecuting jail deputies is difficult because such cases usually must rely on the word of inmates. "Juries don't like to feel that people who are supposed to be protecting us and keeping us safe . . . are suddenly violating the law," he said.

In 2005, a federal jury acquitted two deputies of violating the civil rights of two alleged gang members who said they were beaten while handcuffed in jail. A year later, Deputy Marco Rivas was convicted of misdemeanor assault for repeatedly kicking an inmate in the Twin Towers Correctional Facility.

The inmate at the center of the latest prosecution is hardly a stranger to jail. Vasquez's past convictions include theft, making criminal threats and illegally possessing an assault rifle. Today, he is serving a seven-year prison sentence for robbery, prison records show.

On Jan. 3, 2006, according to court records, Vasquez was moved from a module at Men's Central Jail after he made an obscene gesture at a custody assistant. A day later, he complained that several deputies had attacked him during his transfer to a disciplinary area of the jail. He named one deputy as the main assailant and said another -- Lopez -- later ignored his request for medical help and told him to "suck it up."